Hmm, yeah. "You should write this way, and not that way" says that "this way" is morally superior to "that way". That's classism in culture telling you to not be classist in terms of economics.
And I actually think that some ideas are better than others, and so are some versions of morality. And I think that those who have the better systems should teach them. But they need to do so with a fair amount of sensitivity and humility, not with arrogance.
But then, I'm not the one preaching against classism.